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Frequency Response/Contour EQ in full range systems.
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<blockquote data-quote="Nick Hickman" data-source="post: 35536" data-attributes="member: 556"><p>Re: Frequency Response/Contour EQ in full range systems.</p><p></p><p>Hi Phil,</p><p></p><p></p><p></p><p>But aren't they different beasts?</p><p></p><p></p><p></p><p>I think my point is that if the objective is to exclude late-arriving energy from the measurement, the time window inherent in the DFT won't achieve it. I created a little demo in relation to this years ago so I'll trot it out for your comment.</p><p></p><p>I used Smaart to measure some particular response. The 1/24th octave magnitude view below shows the result in orange from about 1kHz to 8kHz: it's gradually rolling off.</p><p></p><p style="text-align: center"><img src="http://100dB.com/misc/windowrta.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>I then created a copy of the signal that was delayed by 50ms and very heavy in 4kHz and added this in. This is the (exaggerated!) late-arriving reflection that I want to exclude from the measurement. The "RTA" view, of course, includes the late energy and this results in the magenta curve above.</p><p></p><p>I then looked at a variety of transfer functions below.</p><p></p><p style="text-align: center"><img src="http://100dB.com/misc/windowtf.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>The orange curve is the original signal in FPPO mode. It's the same as the orange RTA curve.</p><p></p><p>The yellow curve has the 50ms late-arrival added in FPPO mode. It's the same as the magenta RTA curve.</p><p></p><p>The green and magenta curves are the same thing using a 16K-sample and 512-sample (12ms TC) FT (@ 44.1ksamp/s) respectively.</p><p></p><p>The blue curve is the same thing using a 16K-sample FT but with a 30ms time window (i.e. IDFT, truncate, DFT). This is doing a pretty good job of chopping out the late energy.</p><p></p><p>All the examples have smoothing and a lot of averaging.</p><p></p><p>Interested in your wisdom!</p><p></p><p></p><p></p><p>Absolutely.</p><p></p><p>Nick</p></blockquote><p></p>
[QUOTE="Nick Hickman, post: 35536, member: 556"] Re: Frequency Response/Contour EQ in full range systems. Hi Phil, But aren't they different beasts? I think my point is that if the objective is to exclude late-arriving energy from the measurement, the time window inherent in the DFT won't achieve it. I created a little demo in relation to this years ago so I'll trot it out for your comment. I used Smaart to measure some particular response. The 1/24th octave magnitude view below shows the result in orange from about 1kHz to 8kHz: it's gradually rolling off. [CENTER][IMG]http://100dB.com/misc/windowrta.png[/IMG][/CENTER] I then created a copy of the signal that was delayed by 50ms and very heavy in 4kHz and added this in. This is the (exaggerated!) late-arriving reflection that I want to exclude from the measurement. The "RTA" view, of course, includes the late energy and this results in the magenta curve above. I then looked at a variety of transfer functions below. [CENTER][IMG]http://100dB.com/misc/windowtf.png[/IMG][/CENTER] The orange curve is the original signal in FPPO mode. It's the same as the orange RTA curve. The yellow curve has the 50ms late-arrival added in FPPO mode. It's the same as the magenta RTA curve. The green and magenta curves are the same thing using a 16K-sample and 512-sample (12ms TC) FT (@ 44.1ksamp/s) respectively. The blue curve is the same thing using a 16K-sample FT but with a 30ms time window (i.e. IDFT, truncate, DFT). This is doing a pretty good job of chopping out the late energy. All the examples have smoothing and a lot of averaging. Interested in your wisdom! Absolutely. Nick [/QUOTE]
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